Effective management of soyabean rust and frogeye leaf spot using a mixture of flusilazole and carbendazim

To minimise yield losses caused by an outbreak of frogeye leaf spot (FELS) (Cercospora sojina) on soyabeans in Zimbabwe, crops throughout the country required fungicide applications. Mancozeb, a dithiocarbamate fungicide with contact activity, and two benzimidazole fungicides, benomyl and carbendazim, with systemic activity, were known to be effective against FELS. To avoid the overuse of fungicides in the benzimidazole group, an alternative systemic fungicide group with efficacy against FELS was required. The efficacy of the triazole fungicide, flusilazole, on its own and in a pre-pack mixture with carbendazim was compared with benomyl, on its own, in field experiments in 1996 and 1997. Flusilazole and the mixture of flusilazole+carbendazim were more effective against FELS than benomyl. FELS was managed with two fungicide sprays, the first spray being applied at early flowering and the second, 14 d later.In 1998, Asian soyabean rust (ASR) (Phakopsora pachyrhizi) was first detected on soyabeans in Zimbabwe. Two field experiments were conducted in 1998 and a third in 1999, to evaluate the effectiveness of flusilazole and the pre-pack mixture of flusilazole+carbendazim against ASR. Both flusilazole and the mixture of flusilazole+carbendazim halted the development of ASR. Where ASR occurred late (65 d after planting) and infected mature plants, two fungicide applications 20 d apart were sufficient to minimise the outbreak. Where ASR infection occurred earlier (54 d after planting), three applications at 21-d intervals were required. Three applications of the contact fungicide, mancozeb, also gave effective control of ASR where disease pressure was low.Flusilazole, benomyl and the mixture of flusilazole+carbendazim reduced yield losses caused by FELS and ASR compared with the untreated controls.